The invention relates to a process for the beneficiation and transportation of coal. The term coal in this specification denotes all solid carbon-containing fuels, such as coal and brown coal. These solid fuels generally contain all kinds of components that do not contribute to the combustion value (such as stone, ash, minerals, sand, clay, et cetera). These components can be present in the coal in a mixture therewith and/or enclosed in the coal itself. The term beneficiation in this specification denotes the partial or complete removal of these components and the conversion of the coal into a more manageable form.
Coal becomes available with the most diverse particle size distributions, in the form of lumps, granules and/or powder. Coal lumps and granules occupy too much space during transport, and often contain ash inclusions. It has therefore already been proposed to grind the lumps, to remove the ash and stone, and to transport the obtained coal particles with water as a slurry through a pipeline.
In the German patent specification, No. 1,120,392, it has been proposed to do this in such a way that the particle size of the coal is related to the specific gravity of the coal in a certain way. The present invention relates to a similar process, i.e. relates to a process for the beneficiation and transportation of coal, in which a slurry of coal particles in water is prepared, the large particles having a low mean specific gravity and the fine particles having a high mean specific gravity and in which this slurry is transported through a pipeline.
In the process according to the above-mentioned German patent specification, this special distribution of the coal particles in the slurry is reached by splitting the coal to be beneficiated into two parts by classification according to specific gravity and by grinding the fraction that has the higher specific gravity to a finer degree than the fraction that has the lower specific gravity. The two fractions are subsequently taken up in water so that a slurry is obtained. In this slurry the specifically heavier particles do not sink more rapidly because they are smaller than the specifically lighter particles, so that the slurry is stable.
In practice this proposal is not completely satisfactory because the slurry is not completely stable after all, and the present invention aims at improving upon this situation.